1. Field of the Art
The present invention relates generally to a vacuum conveyor system for transferring workpieces under vacuum (more precisely, under a partial vacuum, i.e., under a reduced pressure), and more particularly to such a vacuum conveyor system suitable for drying or other operations under a reduced pressure.
2. Related Art Statement
Generally, a process of manufacturing an article includes, in almost all cases, a heat treatment step for heating and/or drying purposes. For example, ceramic green pieces are dried by heating workpieces in an atmosphere of a reduced pressure. Under a reduced pressure, the vapor pressure is lowered, and the workpieces may be dried at a comparatively low temperature, with a reduced possibility of chemical changes and cracks of the workpieces. Further, the drying under a reduced pressure may be achieved in a shorter time. In particular, a vacuum microwave heating by means of high-frequency electromagnetic waves permits the workpiece to be heated internally, and assures even or uniform drying of the workpiece with a high thermal efficiency.
Conventionally, such a vacuum microwave heating is conducted in a comparatively large heating chamber which is held under a reduced pressure. Workpieces are placed on a turntable located within the heating chamber, and are irradiated by microwave radiation while the workpieces are moved with rotating movements of the turntable. In this type of batch heating using a turntable, the size and installation area of the turntable must be increased as the amount of processing of the workpieces is increased. However, the installation space in the heating chamber is limited, and consequently the processing capacity of the system is limited.
In the meantime, a microwave heating under the atmospheric pressure is known, wherein a conveyor is used to successively feed the workpieces through a heating chamber. However, the use of such a conveyor for a continuous vacuum drying operation has been considered difficult in view of various problems to be solved, for example, in maintaining pressure tightness of the heating chamber, and in connecting a vacuum pump as a vacuum source to the heating chamber.